"+1 on the Acoustic Imagery ATSAH NC amps, I have had a preview set for a few months as well and as good as the NC400's are, these are a considerable step up.....

I've measured both and the NC1200 based amps don't measure quite as well in nearly all regards except for power. Given my speakers, the difference in power is pretty much a moot point but I know of 5 others who have heard both in the same systems and to a person they all found the ASTAH NC's (1200's) subjectively better."

They are talking about a commercial 1200 ncore product. Curious if anyone has any ideas on why it should sound substantially better than the 400, which has better specs???

Bruno Putzeys was quoted: "It's always a dilemma whether an amp should be tuned for things like subjective bass control, sweet mids or not. --- But it's tough to resist the occasional sonic touch-up. I can emulate the sound of pretty much any amp out there if I wanted. But so far I'm resisting."

"+1 on the Acoustic Imagery ATSAH NC amps, I have had a preview set for a few months as well and as good as the NC400's are, these are a considerable step up.....

I've measured both and the NC1200 based amps don't measure quite as well in nearly all regards except for power. Given my speakers, the difference in power is pretty much a moot point but I know of 5 others who have heard both in the same systems and to a person they all found the ASTAH NC's (1200's) subjectively better."

They are talking about a commercial 1200 ncore product. Curious if anyone has any ideas on why it should sound substantially better than the 400, which has better specs???

I definitely know too little about the test conditions let alone the actual builds being compared to make an educated guess, but IŽd guess that the two amps had different power supplies. If the NC1200 based amp had one dedicated PS per channel and the nc400 instead shared one smps600, that could be an obvious factor.

Also, the ASTAH implementation of the nc1200 boards could be slightly tweaked away from standard to the vendors liking and "house sound"-interpretation of better sound.

If it was possible to test the nc1200 against a bridged nc400 based amp, it could be interesting if the tables turned indicating the sheer tab power/potential voltage swing to be responsible...

quite a few people complaining about heat issues made me look at output transistor type on my UCD180s. at one side there's a 14NF12FP. datasheet lists Ron as 0.14 ohm. a while back while I was working for an automotive company I was curious about the FETs that were driving a 100A motor. I looked them up (don't remember the part code) and they were 1 mohm Ron devices. Farnell has some parts with Ron less than that.
would a lower Ron device bring some benefits, heat-wise?

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we all love a good ol' stereotype until it's against us

I definitely know too little about the test conditions let alone the actual builds being compared to make an educated guess, but IŽd guess that the two amps had different power supplies. If the NC1200 based amp had one dedicated PS per channel and the nc400 instead shared one smps600, that could be an obvious factor.

Also, the ASTAH implementation of the nc1200 boards could be slightly tweaked away from standard to the vendors liking and "house sound"-interpretation of better sound.

If it was possible to test the nc1200 against a bridged nc400 based amp, it could be interesting if the tables turned indicating the sheer tab power/potential voltage swing to be responsible...

This was my comment. I have a Prism DScope III that was used for measurements, along with a nearly non inductive load bank capable of absorbing up to 4kW. My line voltage is generally between 120 and 122V and the shop has a several 20A circuits. I use a laptop on battery power when testing to prevent any PS noise from the computer from affecting the result. I also insert a Prism ds-LPF low pass filter between the amps and the DScope, this is an AES-17 filter designed for use when testing class D amps.

The ATSAH NC amps use the Hypex SMPS1200 PS, one per mono block. The NC400's use the Hypex SMPS600 supplies, again one per mono block, nothing shared. Looking at the data sheets from Hypex it's pretty clear the NC1200 OEM modules measure a little worse in terms of THD but of course they have much more power. I did not do extensive measurements but what I did run agree with the data sheets. The FFT plot of both amplifiers is superb but since the NC1200 based ATASH amps have slightly more THD (per their data sheet spec), the 2nd harmonic is a little higher on the FFT plot, but still very low.

It is my understanding the John @ Acoustic Imagery does not tweak the modules for a house sound.

My NC400's are assembled as prescribed in the data sheets, tightly twisted wiring and such. The measurements for both amps that I have taken match the specs in the Hypex data sheets. The NC400 actually manages a little bit more power than the spec, I consistently see about 240W into an 8R load. I've tested at least a dozen NC400's and they are all very close to the same.

In my system the ATSAH NC (NC1200 based) amps are subjectively superior to the NC400's. The offer greater resolution of low level information, somewhat larger sound stage/image and are subjectively warmer/fuller/richer. The highs also have a bit more open sound to them.

I run both fully balanced from a Krell KCT preamp, main speakers are GedLee Abbey's, so an easy load. Had I not had the opportunity to be a tester for the AI amps, I'd still be really happy with the NC400's.

If the 1200 module specs worse and sounds better, might it be a difference in smps performance? Quite curious as to what could explain this....

I have wondered the same thing myself but not enough to try and build a new PS for the NC400's, which I know some have done. The specs are not very different and low order harmonic distortion is is generally considered benign and in both amps the upper harmonics are buried in the noise floor at least 120dB down. (1W of output).